OFFSET
1,1
LINKS
Peter J. Cameron, Pallabi Manna, and Ranjit Mehatari, On finite groups whose power graph is a cograph, arXiv:2106.14217 [math.GR], 2021. See Theorem 1.3 (a) pp. 3-4.
MATHEMATICA
q[n_] := n == 1 || PrimePowerQ[n] || PrimeOmega[n] == 2; Select[Range[3, 10^4, 2], PrimePowerQ[#] && q[(# - 1)/2] && q[(# + 1)/2] &] (* Amiram Eldar, Jun 29 2021 *)
PROG
(PARI) isor(q) = (q==1) || isprimepower(q) || (bigomega(q)==2);
isoka(q) = (q%2) && isprimepower(q) && isor((q-1)/2) && isor((q+1)/2);
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Jun 29 2021
STATUS
approved